Updating your old furnace will pay you back in savings

If your furnace looks like this, it may be time to consider an upgrade.

Heating and cooling account for about 56 percent of the energy used in a typical U.S. home, making it the largest energy expense for most households.

A wide variety of technology is available for heating and cooling your home, which is capable of achieving measurable efficiencies in converting an energy source into useful heat or cool air. In addition, many heating and cooling systems have supporting equipment, such as thermostats and ducts, which provide further opportunities for saving energy.

No matter what fuel source you are using, the rule of thumb says that if a unit is more than 15 years old it is time to replace it.

The newer, energy-efficient units will greatly reduce your energy consumption, making the pay-back time for the unit very reasonable. A central furnace or boiler's efficiency is measured in annual fuel utilization efficiency (AFUE). An AFUE of 90 percent means that 90 percent of the energy in the fuel source becomes heat for the home, losing only 10 percent of the conditioned air as it escapes up the chimney or through leaky walls and windows.

Older furnace and boiler systems had efficiencies in the range of 56 percent to 70 percent. Modern conventional heating systems can achieve efficiencies as high as 97 percent, converting nearly all the fuel to useful heat for your home. The U.S. Department of Energy developed a table to calculate the cost of savings. If your existing system has an AFUE of 70 percent and you upgrade to a system with an AFUE of 90 percent, you will save $22.22 for every $100 of fuel costs per year.

When shopping for a new furnace, make sure you look for the Energy Star label and make sure the system is not oversized for your house.

Energy efficiency upgrades and a new, high-efficiency heating system can often cut your fuel bills and your furnace's pollution output in half. Upgrading your furnace or boiler from 56 percent efficiency to 90 percent efficiency in an average cold-climate house will save 1.5 tons of carbon dioxide emissions each year if you heat with gas, or 2.5 tons if you heat with oil.

The Federal Trade Commission requires new furnaces or boilers to display their AFUE so consumers can compare the efficiencies of various models. However, AFUE doesn't account for heat or cooling losses in the duct system or piping, which can be as much as 35 percent of the energy for output of the furnace when ducts are located in the attic.

In new home construction or in retrofits, proper duct-system design is critical. Many existing duct systems lose a lot of energy from leakage and poor insulation. Existing ducts may also be blocked or clogged and will benefit from a good cleaning.

Efficient and well-designed duct systems distribute air properly throughout your home without leaking to keep all rooms at a comfortable temperature.

The system should provide balanced supply and return flow to maintain a neutral pressure within the house. Therefore, the placement of the return air ducts is as critical as that of the supply ducts to keep the air flowing well throughout your home.

Ductwork should never be run through an unconditioned attic. This means that if the insulation is laid on the floor of the attic, no ducts should run above it. If you want to use your attic to run ductwork, then the insulation must be moved to the underside of the roof so the conditioned air will not be compromised by passing through an excessively hot or cold space.

Programmable thermostats are another way to save money on energy without sacrificing comfort.

You can easily save energy in the winter by setting the thermostat to 68 degrees while you're awake and setting it lower while you're asleep or away from home. By turning your thermostat back 10-15 degrees for 8 hours, you can save about 5 percent to 15 percent a year on your heating bill — a savings of as much as 1 percent for each degree if the setback period is eight hours long.

While furnaces and boilers can be retrofitted to increase their efficiency, this cost should be carefully weighed against the cost of a new boiler or furnace.

Many manufacturers and dealers offer significant promotions, especially for "off-season" equipment. If you choose to replace your heating and/or cooling system, you'll have the opportunity to install equipment that incorporates the most energy-efficient heating technologies available.

We all know the old adage, "If it ain't broke, don't fix it." However, when it comes to energy-efficient heating and cooling equipment, do some homework to see if it will pay to replace it, even if it 'ain't broke'.

Architects Ann Robinson and Annie V. Schwemmer are the founders of Renovation Design Group, www.renovationdesigngroup.com, a local design firm specializing in home remodels.